1. Field of the Invention
The present invention relates to an apparatus for movably supporting and positioning a transducer which performs magnetic, or optical or other conversion of signals from one physical state to another. Such an apparatus can be used, for example, in a data recording and reproducing system, such as a magnetic disk drive or an optical disk drive.
2. Description of the Prior Art
Recently, modern disc apparatuses record data on a recording medium at a very high density and/or reproduce data from such a medium. A transducer driving apparatus is utilized to position a recording/reproducing head at an extremely fast speed and with a high precision on the track of the recording medium.
Referring now to the accompanying drawings, an example of a conventional transducer driving apparatus is described below, which is disclosed, for example, in the Japanese Patent Publication No. 63-119026 of 1988.
FIG. 7 illustrates an example of a conventional optical transducer driving apparatus. Typically, the conventional optical transducer driving apparatus includes a chassis 32 which is secured to an optical head mechanism of an optical data recording and reproduction apparatus by an appropriate means. The L-shaped supporting base 34 is secured to the chassis 32.
One end of the elastic plate springs 36a and 36b are respectively secured to both ends of the L-shaped supporting base 34. These elastic plate springs 36a and 36b are respectively provided with slits to facilitate deforming thereof into a bellows form.
The other end of the elastic plate springs 36a and 36b are respectively secured to the opposite sides of the rigid interim member 38. One end of the elastic springs 40a and 40b are respectively secured to the upper and bottom surfaces of the rigid interim member 38. The other end of the elastic plate springs 40a and 40b are respectively secured to the upper and bottom surfaces of the lens holder 44 holding the lens 42 which focuses and radiates a light beam onto a recording medium to implement recording or reproduction of data.
As shown in FIG. 7, the focus-drive coil 46 for driving the lens 42 in the focussing (z-axial) direction is secured to the external lateral surface of the lens-holder 44. Furthermore, four units of the tracking-drive coil 48 are secured to the external circumferential surface of the focus-drive coils 46. These four tracking-drive coils 48 are provided for driving the lens 42 in the tracking (y-axial) direction. An end of the power-feeding wire 49 for feeding drive current to these tracking-drive coils 48 is secured to the chassis 32.
A magnetic circuit (having one side which is not shown in FIG. 7) is composed of the permanent magnet 50 and the magnetic yoke 52 and is installed in a position opposite the coils 46 and 48 in the x-axial direction.
Referring now to FIGS. 7 through 9, the functional operation of the conventional transducer driving apparatus incorporating the above mechanism is described below.
As shown in FIG. 7, when the power is delivered to the focus-drive and tracking-drive coils 46 and 48, electromagnetic force is generated by the magnetic circuit composed of the permanent magnet 50 and the magnetic yoke 52. As a result, the plate springs 36a, 36b, 40a and 40b elastically deform to drive the lens 42 in the tracking (y-axial) direction and the focussing (x-axial) direction.
Next, the function of the plate springs 36a and 36b deforming into a bellows form is described below.
FIG. 8 is the plan view designating the deformed status of the plate springs 36a and 36b of the conventional transducer driving apparatus. As shown, when driving the lens holder 44 in the tracking (y-axial) direction, the plate springs 36a and 36b deform themselves into a bellows form on the plane by the effect of the slits provided therefor. Nevertheless, since the above structure provides such slits 60 for deforming the plate springs 36a and 36b into a bellows form in the tracking (y-axial) direction, the rigidity of these plate springs 36a and 36b in the focussing (x-axial) direction is insufficient. In particular, due to the weight of the movable part at the tip edge of the lens 42, when the deformed volume grows in the tracking (y-axial) direction, a moment force is generated in the periphery of the x-axis. This in turn causes the plate springs 36a and 36b to incur torsion. As a result, the optical axis of the lens 42 falls, thus resulting in an unstable control over the tracking/focus positioning. To solve these problems, a conventional art has been introduced to prevent the occurrence of torsion by reinforcing the thickness of the plate spring. On the other hand, although torsion can hardly be generated when reinforcing the thickness of the plate spring, oscillation proper to the plate spring increases to result in a lowered DC sensitivity in the tracking (y-axial) direction.
In other words, expansion of the thickness of the plate spring conversely increases the power consumption per unit transfer.
Even when the length of the plate spring is extended to solve the problem, such counteracts the needs for providing a compact transducer driving apparatus. Further, when transferring the movable part of the tip edge of the lens 42, the power-feeding wire 49 behaves as the externally disturbing load which adversely affects the high-precision positioning of the transducer driving apparatus.
To dispense with the plate spring, conventionally, it is known to support the movable unit by means of a bearing. However, due to the mass of the bearing and the load caused by the friction force of the bearing, actually, the weight of the movable unit can hardly be reduced, and yet, the movable unit cannot easily access at a very fast speed. Furthermore, any conventional transducer driving apparatus cannot be positioned with extreme precision because of the wobble of the bearing and resonance generated by the twisted movable unit.